The invention relates to a process for determining and monitoring a contact point of an automated clutch in a motor vehicle. The invention also relates to a computer program product and apparatus for determining and monitoring the contact point of an automated clutch.
The DE 102 48 195 A1 discloses a process for monitoring a function of a motor vehicle control unit.
The application area of the invention is the control of twin clutch systems and related automated clutch systems in automobiles. The invention is a safety function and serves as a component part of a safety system for guaranteeing functional safety of twin clutch systems and related, automated clutch systems.
In principle, safety functions are designed such that so long as no error is indicated by the safety function, no error prevails in the process carried out and/or monitored by the safety function and system with which the process is carried out because all actions or reactions of the system are considered with respect to the process.
In modern motor vehicles, automated clutches, i.e. clutches operated by actuators, are increasingly finding application. The position of an activating element of the clutch or actuator respectively is mostly recorded with the help of an incremental counter that directly delivers only the information regarding the regulated distance just covered; however, it does not deliver information about the absolute position of the activating element. In order to find the absolute position, referencing is required whereby a predetermined activating position of the clutch is approached by the actuator and the respective count of the incremental counter is read out.
The same problem is posed by actuators with an absolute distance measurement and is not necessarily coupled to the incremental distance measurement.
A fundamental problem of such incremental distance measurements is their dependence upon exact determination of the reference position. This problem is aggravated in that for vehicle operation, the occurrence of error events must be inherently expected, which can lead to the absolute position of the clutch actuator or respectively of the activation element of the clutch not being known and thus also the clutch torque setting by the actuator in the electronic control device is no longer known. Critical events relating to safety can result from this, for instance, the vehicle starting to move without the driver's intent. An exact knowledge of the respective activation position of the clutch in a twin clutch transmission is particularly critical to safety in which two clutches must be actuated in an accurately coordinated manner.
For the control of automated clutch systems, for instance, automated manual-shift transmissions with a single clutch or twin clutch systems, the so-called contact point is a central quantity. It describes the position of a clutch, from where the latter begins to transmit a definite, low torque—normally about 5 Nm is selected. Among others, this position is therefore important in ensuring functional safety.
The contact point is learned during the first start up operation by each of the two clutch systems in the twin clutch system and stored in the system. This one-time learning would neither fulfill the comfort nor the safety requirements for the system, since the contact point, due to the system and ambient conditions can already fluctuate within a driving cycle and changes also in the long term over the lifespan of the system. For this reason, there are complex adaptation and compensation strategics in the control software of twin clutch systems, which have the target of determining the current contact point as accurately as possible.
If these strategies would lead to incorrect determination of the contact point, this can, in the worst case, lead to safety critical situations. The clutch would transmit different torque at the contact point than what is expected. The functional safety for the twin clutch system would be in question.